This invention relates generally to audio signal processing systems; and more particularly to signal processing systems involving movement of such signals.
Music, whether it be classic, folk, rock, pop, or another form, has long interested audiophiles, both in its "live" form and recorded arrangements. One of the most difficult tasks in recent years has been to convey the musician's art to all portions of his audience in a manner which pleases each portion thereof, whether the musician's art is "live" or recreated.
Where the music is live, most efforts have been directed to distributing the sounds to all portions of the audience uniformly, so that each member of the audience hears substantially the same sounds, at any given moment, as every other member of the audience. However, the inherent limitations of two- and four-channel systems have prevented each member of the audience from experiencing the same sounds as any other member of the audience. More particularly, listeners placed, respectively, closer to a first speaker system and a second speaker system will hear substantially different sounds, assuming that the signals provided thereto are at least stereo. Thus, the optimum signal is perceived from only limited positions of the audience.
In recreating recorded music, the effort has thus far been directed to reproducing the "live" performance. This of course has the attendant limitations of limited optimum listening positions, although it is possible to adjust the amplifiers and speaker systems to provide optimized listening at a given location. Nevertheless, other positions in the listening space are non-optimum; thus, despite the adjustable nature of the system, substantial limitations still exist.
In connection with the typical, unachieved concept of distributing the sound equally to each listener, it has been usual to maintain at as constant level as possible the audio signal to each channel, varying levels only as necessary to accurately recreate the live performance. In some instances, the number of channels has been increased, e.g., "quad", as shown in Iida U.S. Pat. No. 3,725,586. In some instances, however, the signals to the various channels have been varied to attempt to provide "movement" of the sound, as for example in Raydon U.S. Pat. No. 3,969,588; Wedan U.S. Pat. No. 3,873,779; Weiss U.S. Pat. No. 3,982,071; and Williams U.S. Pat. No. 3,757,046. Other devices have employed phase shifting circuits to provide azimuth representations, as for example Gerzon U.S. Pat. No. 3,997,725. In other instances, loudspeakers have been arranged to give the illusion of fullness, or naturalness, by disposing the loudspeakers in a three dimensional arrangement, as for example Bucky U.S. Pat. No. 2,179,840 and Schaeffer U.S. Pat. No. 2,636,943.
However, each of these systems suffers from a variety of limitations. Typical of these limitations are lack of smooth transitions between speaker systems, and limited forms of movement. In addition, movement of a plurality of independent signals through three dimensions has heretofore not been possible. Also, in those systems which have involved rudimentary sound movement techniques, such movement has been preselected or fixed, and not dynamic. Because of these and other limitations, there has been a need for an improved audio imaging device.